SilverG33k:


You can use FireBase to achieve this!!

.......

Refreshing every 1 seconds even when nobody is online is bad so make it 4 - 10 seconds WHEN at every 60seconds interval, there is a user online waiting to send message.

This means that it is when a user is online that you run a timer of 4 or 2 seconds interval, instead use a 1 minute interval to check if any user is online at all. Use a background service and Timer to continue running every time to fetch data and when there is a new message, display the message....

I don't want to use firebase I want to use Json php and mysql am designing d charting part I will post d source code soon

My suggestion is to use a firebase real-time database for creating the instant chatting app. you can easily develop chatting app using the firebase database.
If you are an experienced developer then you can go throw the MySQL database. I had implemented chatting functionality in one of my android projects using MySQL database, you can download a sample app or source here.
https://itinsidenews.com/mymall-android-app-free-source-code